Medical workers assist a patient into an ambulance during an evacuation of New York University's Tisch Hospital, Monday, Oct. 29, 2012, in New York. The New York City hospital is moving out more than 200 patients after its backup generator failed when the power was knocked out by a superstorm. (AP Photo/ John Minchillo)

NEW YORK (AP) — A backup generator failed at a New York City hospital, forcing it to move out more than 200 patients, including 20 babies from neonatal intensive care.

About two dozen ambulances were lined up around the block outside New York University Tisch Hospital Tuesday morning. Doctors and nurses began the slow process of evacuation Monday night, starting with the sickest and youngest. Some were on respirators operating on battery power.

Officials said all but a handful of patients were evacuated by Tuesday morning. The remaining few were in rehab or were epilepsy patients on the 12th floor.

"It’s a challenging situation," NYU Medical Dean Robert Grossman told WCBS-TV. "We drill all the time for this kind of thing. But this isn’t a drill. This is the real thing."

Much of New York was plunged into darkness by superstorm Sandy, a monstrous hybrid system that swept across a huge swath of the East.

Most of the power outages in lower Manhattan, where Tisch is located, were due to an explosion at an electrical substation, Consolidated Edison officials said. It wasn’t clear whether flooding or flying debris caused the explosion, said John Miksad, senior vice president for electric operations at Con Edison.

Without power, there were no elevators, meaning patients — some of whom were being treated for cancer and other serious illnesses — had to be carefully carried down staircases, Grossman said.

As the patients were evacuated Monday night, gusts of wind blew their blankets. Nurses and staff huddled around the patients, some holding IVs and other equipment.

Ambulances came from around the city to help transport the sick. Patients were taken to other hospitals including Mount Sinai and the Memorial Sloan-Kettering Cancer, Lenox and Bellevue.

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